This relates to electronic devices, and more particularly, to electronic devices with component mounting structures that help the electronic devices withstand damage when subjected to stress.
Electronic devices such as computers, media players, and cellular telephones typically contain electronic components. For example, a handheld electronic device might contain an accelerometer module that is used in determining the orientation of the handheld electronic device with respect to ground (e.g., whether the device is in landscape or portrait mode). Accelerometers and other electronic components such as integrated circuits, microphones, speakers, status indicators, and connectors for input-output ports, are typically mounted on printed circuit boards. Conductive traces on the printed circuit boards are used to route signals between the components.
Components are often mounted to printed circuit boards using solder balls. For example, a “flip-chip” arrangement may be used to mount an integrated circuit to a printed circuit board. With this type of configuration, an array of solder bumps is interposed between the integrated circuit and the printed circuit board. The solder bumps serve to electrically connect the circuitry of the integrated circuit to the printed circuit board. The solder bumps also serve to physically attach the integrated circuit to the printed circuit board. Components such as accelerometers may also be mounted in this way.
Electronic devices and the electrical components within these devices are sometimes exposed to large stresses. For example, a user of a device may inadvertently drop the device on the ground. When the device strikes the ground, the printed circuit board and the components mounted to the printed circuit board are subjected to stress. If the stress is too great, components may become partly or fully detached from the printed circuit board or may become damaged due to internal stresses.
One way in which to enhance the robustness of a typical solder ball component mounting scheme involves the use of epoxy underfill. During manufacturing, liquid epoxy is introduced into the gap between a component and the printed circuit board to which the component is mounted. Capillary action draws the epoxy between the component and the printed circuit board. The epoxy is then cured, which helps stabilize the mounted component and prevent inadvertent detachment of the component during a drop event.
Underfill arrangements are often satisfactory when mounting robust components to a printed circuit board. However, underfill arrangements are not satisfactory for use with sensitive components such as accelerometers. When components such as these are underfilled, the presence of the underfill disrupts proper operation of the component. Proper operation can be ensured by omitting the underfill when mounting the components, but this tends to increase the risk of component failure during a drop event.
It would therefore be desirable to be able to provide electronic devices with improve component mounting structures.